Selective-switch-controlling system



N0v.1, 1927. 1,647,373 F. N. REEVES.

SXJJECYIVE! SWITCH CONTROLLING SYSTEM Filed June 2l, v1924i 2 Sheets-#Sheet 1 NS; a@

by Ariz/ Patented Nov. l, 1927.l

`viiaiiiviz N. REEVES, 0E WoonENsBUnG, MARYLAND, Assicriion To WE'sTERN'ELEoTRic, GQMPANY, iicoiiPonA'iED, o'E'NEW YoRK, ii. Y.,'Aconi onar1oi\i '0E 'NEW-YORK. 'i

SELECTVE-SVVTCEE-CONTROLLING SYSTEM;

Application iled June 21, 1924.. SerialNo. 7215382.v Y

'This invent-ion relates to aA telephonejexchange vsystem and more particularly to selective sWit-chesfoi use'in a machine switching system.

' It is an object otliis inventionto provideA an improvement in selectiveV switch control. n machine switching systeiiis"'varioiis types of selective switches arev used toasso.-

ciate a calling` With a called line. One type of selective sivitcheslare equipped with a plurality'ot movable brush, members', each 'brush memberbeing associated with a particular bank of terminals. These selective switches are Vdirected to select a particular bank ot terminals by an operation known as brush selection. T his operation constitutes the positioning of a4 particular one of the plurality of movable brush members in such ymanner that the contacts of the brush member may bei tripped. The tripping operationcontrols the association ot the particu- 'lai brush contacts with the ytirst set of terminals in a bank. Upon the complet-ion of brush selection,'tlie selective switch is operated Vto select a `groupof terminals Within the bank over which thetripped brush meinber may hunt for an idle4 line. y o

Each bankr in a rframe' is 'usuallydivided into sever-,alfgroups of term'iiialsvin aV uni- Vmember. Large groups oi lines extending` lfil) to yparticular oiiices require a plurality of ips of t terminals ina bank and plurality of 'gr-oupsare therefore` combined into one group known asA an oii'ice group. In such etilico-groups, it 1s desirableto connect lines vto the intermediate unused overfloiv terminals.V l/Vithin the knowledge or" the applicant. this has not been done heretofore, since the oliicepgroups couldnot be economically arrangedlin thev same mannerin each of theA plurality of banks and means were not vprovided to lcontrol 'the oveiliow segments of the commutator to make it flexible for the control oil/the selective sivitchivhen its movablebru'sh members Were associated with any ot-the vplurality of'banks of terminals.

A feature loft-his invention is in the provisionv ot means vfor controllingvselective knovvn sequence' vsrvitch type. switch 220 is ofthesame gene'r'aIt-ype shown f `in Patent 1.12.?6965` issuedfJanuary 5f, 1915.`

toE. B.; Graft et al. The' brush members .ot f the selector switch are cquipped'ivith-a consivitch operation in accordance VWith theoperation 'ot al particularbrush as `asso'ciated ywith a particular. bank of terminals-;

This and other featuresv of the 'i invention Willbe apparent in theifollowingdescription` taken in 4connection with the accompanying drawings.V

While the invention .has beenf'disclose'd as particularly; adapted for the operationV and control of selective switches-1in"avmachine switching system, it `isapparentfrom the following descriptionthat lthe ir'iventioiil has a Wider utility and that'byslight,modiiica- "tions, it could bcladapted for-control ofap-y parat'us in other types of systems.y

illustrates diagrammatically, algsubscriber-vs switch 102, and sender 103. yFig.*i2-'illus'.-`

trates an oiiice selector switch and associa ed 1 circuits 'arranged to disclose the," invention. Fig. 3

brushes in thetripped, position. l

Descriptionof apparatus; i The :apparatus sho-ivn in v1. loiffa` well known/type and is thesaine as'disy*closed inthe vPatent 1,395,977, ,issuedNov 1,

of magnet 26.1. v Switch 200- isqoi the Well i fSeleCti/' tactto establish a circuit for selective switch -control When theV brushimembers arelbrought into engagement vvthlthe terminals ofa multiple bank. Commutator 270 is equipped yWith aV specials' segment 2113 not ordinarily usedivith, such".commutators The vconducting segments ofl commutator segment. 2,42 cont-rol the 'operation of sivitch26 0fto 'porsibrush member..

v.Fheibrush set'255 `shows 'a set ofV brushes oft-lie switch" *22.0V with theybrushes in` thefnormal 'un-l H1Q21Wto F..zfStearnl-andlAJScudder. 'A Switcliz260 i's'o'flthe step-by-step type oper.-l

ated by t-lieeiiergization and deeiiergizationIY -i mi Y hasibeen shovvnlinv Y Sto lillustra-te thebrush assembly andfvassof-w .Y ciated contact and (itsfrelationeto'the terminals, of the multiple banlnf V`.ln` this illusiio tration, the trip linger 249 has not engaged the lever arm 248 to cause its operation. This set has been shown in Fig. 4 to illustrate the brush lassembly and associated con-- tac-tatter trip finger 219has engaged leverl arm 248 and caused its operation to assoc iate the brushes with theterminals ot a multiple bank and to close the contact associated therewith. Brush set 255 illustrates the one of a plurality otsuch brush sets assembled in a selective switch that has been selectedto `be brought into engagement with the terminals of a multiple bank.

l General description.

1n accordance with the invention selective switches of a machine switching oliice are associated with trames sub-divided into banks et terminalsthe banksin turn being sub-divided Vinto groups. Each selective switch has one set `of brushes tor each bank of i'nultip'le terminals in order that a particular brush set may be associated with a particular bank and is first directed by a sender to position the particular brush set 'tor cooperation with its bank oi' terminals.

After ar particular brush set has been propcrly positioned, the brush members ottlic brush set are tripped to bring them into association with the terminals ot the bank.

Upon the completion of brush selection, the

selective switch is directed by the sender 'to make group selection to posit-ion the selected brushesv upon the first terminals ot a selected group.V The selective switch is then operr ated to cause the particular brush set to move upward to select an idle line.

lGroups of lines extending to distant otiices are of various sizes and when groups of the same number of terminals are distributed over abank of terminals, the hunting for an idle'lliiie is limited to that group. 1t often happens that all ot the trunks in one group may be busy but there are trunks in a different group to the same oilice which are not busy. An overflow Vterminal-is used at the top of each trunk group to arrest the upward movement ot 'the Vselective switch and thus arrest its hunt'for an idle line. In order tov eliminate certain overflow posit-ions in large'tru'nk groups and use the positions Vfor lines extending to a distant oiiice, this invention provides La means whereby the overtlow positions may be eXible, any one of which will be used `for lines orv overiiow in accordance with the strapping of the terininalsassociated with the brushes of switch y overflow terminals in that particular bank.

l/Vhen the selective switch has been arrested with its tripped brushes upon the first terin order not to encumber it with details which are the saine as disclosed and described in the aforementioned patent No.

1,395,977 to F. A. Steai'n et al.

Let it be assumed that a subscriber at station '100 has removed the receiver from the switchhook preparatory-to initiating a call. Line switch 101, district selector switch 102 land sender 103 are thus associated as shown in Fig. 1 and relay 110 is operated. The subscriber now operates the dial in accordance with the number of the line wanted. The operation of the dial actuates relay 101i ot the sender 103 over a circuit extending from grounded battery through 'the winding of relay 1011, lower contact of cam 112, lower contact of relay 110, Contact of dial, upper contact ot relay 110, lower contact oi cam 111 to ground through balancing coil 103. Relay 10% is operated and released upon each interruption ot the dial cont-acts to set the register switches ot the sender. lVlien the register switches have been set, the sender is advanced Vto a position for associating the district selection switch 102 in a manner to control its upward movement for brush and group selection. Upon the completion of group selectioin'brushes 121, 122 and 123 are brought into engagement with a bank oit terminals associated with. oiiice Vselector switches and the district selec-- tor switch is positioned to control the upward movement ci its yassociated brushesin such manner that an idle otrice selectorV switch is selected. Upon the selection or an idle otiice selector switchHr such as shown "in Fig. 2,`th'e district slector 102 advances its sequence switch to posit-ion 10 in Vwhicliposition the sender 103 may control the selective operation oit the apparatus shown iii register switches.

Upon the association of brushes 121, 122

and 123 with terminals 124, 125 and 126, the fundamental circuit is established to operate relay 271 and stepping` relay 107. This circuit may be traced from grounded lbattery through kthe right winding of relay 271, lower contacts of cam 210, coiiductor'272, terminal 126, brush 123, lower contact oit cam 115, windings of the polarized relay 105 and stepping relay 107, Contact ot counting relay 106, upper contact ot cam'116, brush 122, terminal 125, conductor 273, right upper and left lower contacts of cam 203 to ground. The current flow in the ciriic cuit tracedis not in the proper directionto operate polarized relay-105. y The yoperation of relay 271 establishes a-ci'rcuit to energize sequence switch magnet201 fromV grounded battery through the winding Vo lmagnet 201, lett lower contact of cani 212 to ground through the right outer cont-act of relay 271. Sequence switch 200 now" rotates from position 1 to position 2. The operation of relay 271further'establishes a locking circuit `ioritselifirom grounded Ybattery through its right windingand rightinner contact,

right lower contact of cam 207, conductor '27.2

and thence to ground over the u'ndaiiientalA circuit previously traced. Rel'ay271 is thus maintained vin'V an operated position until the fundamental circuitis o peiied at the con'-A -tact of counting relay A2106. In position 2 ont tliesequence switch 200,' af-circuit is estab lishedfto energize the up-drivemagnet222 `from grounded battery through the winding of this magnet, upper contact or cam 212 to ground through the right outer contact'of relay 271. The selector-switch is now driven invan upward movement and brush 240 is advanced over commutator 244, ywhich has conducting and non-conducting segments.

mental circuit.

The initial engagement of brush 240 with commutator 244 establishes a circuit to shunt the stepping relay 107 in the sender by the associationof a ground with thef fundaground through 4the lower contact of cani 213, brush'240, commutator 244, left upper and lower contacts of'cain 210,`and`thence to a junction point with the undamentaleircuit to cause a release of the sender stepping relay and to maintain relay 271m anoperated position. The operation and release of the senderrstepping relay 107operates counting relays'in the 'sender circuit in va well.

`nown manner. Vhen anumber of counting relays havebeenoperated in accordance with the settingvcf the` sender register,{ the fundamental circuit is opened yat a contactof the Oy counting relay`106.l The holding cir-V cuit for relay 271 is thus opened to cause` its release. The release otrelay 271 opens the energizing circuit-for up-drivemagnet 222' to arrest the upward movement of theV brush `members and commutator brushes. The release-oi relay-271furtherl establishes an energizing circuit to rotate' sequence switch 200 yfrom position 2 to position'. This circuitmay be traced from grounded battery through the winding of V:sequence switch niagnetf201, upperlle'lit contact of cam 209 to ground throughthe right `outer normal ccntactoitl relay 271. During the ro# 4tation or" the sequence switch, the 'sender l103 has operated'to re-position its apparatus and Irelease the counting relays.

X/Vhen `thesequence switchy 200.k rotates to position, thevv fundamental circuit is again festablishedto operate-relays271 and107l in This may be traced from the manner previously. described for the esu -tablishment` of circuits for "oiiice group selection. I Thelocking circuitV for relay 271 is again established *asv previously described. The operation of this relay'establishes an energizing circuittoffrotate sequence switch 200 from position 3 to position 4.v This cir cuit may be ttraced lfrom grounded battery through the winding of 'magnet 201, left lowerl contact of cani 212 to groundthro'ugh v ,f

the -rightlouterc contact otrelayj271. i

In' positions-3 and 4V of sequenceswitch 200, a :circuit'is established to energize ltrip magnet V22S-from grounded battery through the winding of! magnet 223 to jground through the right lower contact of cai`n121'1'.

The energization of'tripmagiiet 223 rotates theztrippingspindle257 to engage the trip nger such as 249 with a. lever arm'such as;

248A.'V A plurality of movable-'brush members su; h as 255 and 256 equipped with cainnle'v'f ers such as 248 are'assembled into each set lectivo switch. The brushselection .previously described is tor thepurpose of bringing the movable brush sets into 'such relation with the trip lingers of the tripping spindle '0r-flv no! that only one ot a plurality of trip lingers will vengage the lever arm ofoneY brush set. V Vilithsequence switch 200 in position 4,' and'relay 271 in an operated position, a circuit is established to energizeup-drive magnet. 222 from grounded batteryjthrough y the winding of the up-drive magnet, upper contact or" cam 212 to ground through the i a n I gization otup-driveiniagnet 222`drives'tlile Y rightouter contact of relay 27-1. Thefenerbrush assemblies inan upward movement. Duringthisl upward movement, the trip tinvger 249 -actuates'lthe particulariever .arinY 248 toas'sociate the .brushes with the ter.-

magnet 222 land thus arreststhe upward movement of the switch sha-ftand the com- ,inutato'rbrushes v i Y Let'lt be SSimleCl .that brush "set 255 was The releasel o1 relay 271v yminals of the banlr multiple.v v'The tripping not' 'tlielbrushes alsoV effects "the closure of L y utility of which will.

tripped as hereinbeiforedescribed and-that .brushes'225, 226 Iand'227 are now'associated Y' .-.f

with the first terminals of ,a group ot lines extending. to a particular oiiice.- Also that theicontact; 224l .isfclosed The otlice cir-v cuit,z Fig-. 2 yis thus .prepared to Ahunt .for .an idle line extendingtoc that particular office.

` movement lof the switch shaft :tor group setact o't cam 213.

lection, brush238 engaged commutator V2 42. Upon eachassociation ,01' :brush 238 with a conducting portion of commutator 242 magnet 261 is energized to attract its armature `to prepare `tor a forward stepping of brushes 263, 264- and 265 .and upon each engagement ot brush 238 with aninsulating portion ot commutator 242, opens the circuit oi' magnet 261 to Acause tnereiease or magnet k261 v and the step by step advance o't' switch 260. During the engagement oit brush 238, with a-conducting portion of the commutator, the circuit for energizing magnet 261 may be traced from grounded battery through its winding, commutator 242, brush 238 to ground through the lower con- Vhen this circuit is opened, magnet 261 releases to rotate the brush assembly 263, 264 and 265 one step. ln this manner each v.engagement otbrush 238 with conducting and non-conducting portions o'tb commutator 242 advances the brush assembly of switch 260 one step. Commutator 243 matches commutator 242 withrelation to the number ot conducting and non-cnducting portions. These com mutators are made with a comparatively large number of sub-divisions in order that the line grouping may be made more leXible. A group ot' lines extending to an oiiice may include one or a plurality ot the sub-divisions and this invention proposes to mark vthe size 01"' the groups in the various banks ot' terminals through the association ot switch 260 with commutator 242 which is common to all banks.

1t will be noted vthat certain contacts associated with brushes 264 and 265 are strappedand the straps are associated with relay 270. The number of `contacts between the terminals Athat are strapped indicates the size of a group ot trunks since each icontact represents one step of switch 260 which is operated upon the associa-tion of brush 236`with a conducting portion of commutator 242. Switch 260 is started from its normal position for all selections and is stepped to the first terminal ot a certain oitice group during group selection.

Since it has already been assumed that the brush set 255 is the one used for this selection, contact 224 prepares a circuit path through brush 265 and its associated contacts which Ais V not eii'ective until the sequence switch arrives in its sixth or-trunk hunting position. Let it further be assumed that during group selection brush 265 was rotatedto its seventh position which is not strapped to relay 270.

lt will be remembered that upon the completion ot group selection, relay 271 is released. lThe release of relay 271 establishes a ycircuit to rotate sequence .switch 200 from position 4 to ,position 5. This circuit may betraced from grounded battery through the winding of magnet 201, left upper contact of cam 209, to ground through the right outer normal contact of relay 271.V Inposition Y5, a circuit is established to operate relay 2711 trom grounded battery through its lett rwindingto ground throughthe lower contacts ot cam 203. The operation ot relay 271 establishes a circuit to further rotate the sequence switch from yposition 5to position 6. This energizing circuit may be traced from grounded batterythrough the winding of magnet ,201, left lower contact ot cam 212 to ground through theright outer contact of .relay 271. Upon the rotation of the sequence switch from position 5 to. position `6, the energizing circuit for relay 271 is opened at the lett lower Contact of cam- 203. yRelay 271, however, is maintained in an operated position by a locking circuit, if the first terminal ot the group is characterized by a busy ground. This holding circuit may be traced from grounded battei-.y through the right winding, right inner contact and left contact of relay 271, lower .contact Ioit cam 206, right outer normal contact ot' relay 270, brush 225 to ground upon the sleeve terminal ot the busy line. This holding circuit is further established from 9 the right contact of relay 271 through the upper contact of cam 207 to the busy ground as previously traced.

Let it be assumed for this description that allot the lines in this group gre busy. The continued energization of relay 271 establishes an -energizing circuit for up drive maglati net 222 from grounded battery through the fwinding ot magnet 222, upper contact of cam 212 to ground through right outer contact of relay 271. During the upward mov-ement of 4the selector switch shaft, brush 238 is lassociated with conducting port-ions of .commutator 242to i'urther rotate the brush assembly ot switch 260. Eacho't such engagements advances brush V265 one step as hereinbefore described. lli/Then' brush 265 has advanced two steps, it is associated with the ninth position terminal which is connected to the Y,winding of relay 270 to complete a circuit for its operation. This circuit `208 andfinattracting its right out-er armature Yopens the holding vcircuit for relay 271 to cause `its release. The/release of relay 271 opens the energizing circuit for the up drive magnet 222 to arrest'the upward movement of the switch shaft and the commutator brushes. The circuitV established through ground through the right outerv normal cony the right inner Contact of relay 270 willbe described later. The release of relayv 271 establishes a circuit to rotate the sequence switch from position 6 to -position 7'rom grounded battery through the winding ofV magnet 201, left upper Contact ot cam 209-to tact ot relay 271.- In sequence switchv position 7, a circuit is again established to energize relay 271 .from grounded battery th'rougli'its leftvwindin'g to ground through the lower contacts of cam 203. .The operation of relay 4271v establishes a circuit'to ro-tate these- 4quenc'e switch to position 8. rThis circuit maybe traced Jfrom grounded battery through the windingV oitmagnet 201, lett lower contactof cam 212 to (ground Vthrough the right outer contact'ot relay 271. A holding circuitis established for ,relay l271 trom ground-ed battery through its right winding' and right inner Contact, left lower contact of cam 207, terminal 124, brush 121, contactot cam 117 to ground through the contact ot' relay 130 which is in an operated position. It will be remembered that 'thesequence switch of theV districtl selectorFigure 1 is in position 10.

and 243, a circuit is established to energize e magnet 201 from groundedbattery through its winding, right upper contact'of cam 209,

`.right inner contact of relay 270, coinrnutator V244brush 240 to Aground through the lower contact of cam 213. The sequence switch Ynow rotates from positionS to position 9 under the control ofthe circuitv traced and from position 9 to position 11 under the controloi master' contact 202. In sequence switch position v11, a circuitis established, to.

- operate polarized r-elay 105 in the sender 103. This circuit may be traced froingrounded battery through the lett winding of 'relay 271, right contacts of cam 203, conductor.

273,',terniin'al 125, brush 122, upper contact of--cam 116, contact ofY relay 106,y winding of relay 107, winding ofvrelay 105, lower contact of cam 115, brush 123ter1ninal 126, conductor 272, left contacts oi cam 210, comvinutator 244, brush, 240 toV ground through the -lowercontact of cam 213. It will be noted that the direction of current. iiowv is opposite to that usedforgthe control of the *selective Vswitch Figure 2, and y is in the proper direction to operate the polarized @relay in the sender. The operation of relay h105 advances the'sender apparatus in the manner rdescribed in -the laforementioned 1 -Patent 1,395,977 to F.:A. Stearn et al. and

the @drame-0f the Sender Controls thedstrict selector 102 in such lmanner that itsl sequence switch' is advanced vto position 16.-

In vposition Y16 of the district selector, atene circuit is associated with the ytip and V'ring conductors by induction from lthe left tofthe 17o right winding of coil: 118.y "This mayA beA tracedtroin grounded battery through tone e y repeating coil v118, vcondenser 119, contacts of cain 113, right lower windingV of repeating `coil 1120, Ycondenser 1,30, rightupper `winding of repeating coil to ground through contor and sender arerestored tofnormal.

The rotation e ofV the districtl sequence switch out oi position 10,opens the hol-ding circuit for relay 271 to causeit's releasell A vcircuit is thus establishedtorotate sequence switchj200 fromyposit'ion 11l to' positionf18. This circuit maybe traced from groundedv `tact of cam 114. yThistone is'ca'rri'ed by induction into the left windings of lrepeating "coil 120and is` thus "trans`mitted to ythe V"call-1 jing subscriber as an audible vsignal indicating that! the called line cannot bereached. The subscriber restores the receiver to the switchhook and the apparatus f of the district selecbattery through the winding ,of magnet 201, j left upper contact of cam 209 to ground cuit'is establishedto Aenergize the downdrive magnet 221;l from grounded` battery through they windingy of said magnet to ground' through the contacts of earn 213. The selec- -through the right outer normalj'contactj'ot 1 y relay- 271. [Upon reaching position 18`,al cirtor Vswitch 220 now'restore'djto its 'normal position and brush 239 is associated withl AV circuit is thus' estab` lished to energize the sequence switch to re-l coininutator 246.

store tol normal which may Vbe 'traced'frorn grounded 'battery through the winding `of magnet 201, lower contact of 'cam`209,'cornmutator 246, brush 239, to ground through the Vlower contactof cani l213.V In vpositions 18 to 1 011- the sequence switch, a circuit `is established'to restore Vswitch 260 to normalby the energization of magnetA 261. This circuit may be traced from` grounded vbattery through the winding of said inagnet,.s'felf-v interrupting contact 262', ybrush'2'63 and its lassociatedcontacts to ground throughthe p upper contact of cam 208.k

.By the provision of aseparate are andassociated brush such vas v*264.or"each of the tive brush banlrsof the selector the sizeof the groups lin' each 'bank'ma'y be" variedby changing the strappingin the"Y arc -oif vswitch 260 ,pertaining to such, bank.v f

Itis apparent-trom the foregoing that a control circuit ,established when selector .switch brush selection takes placelrnayibe used to control. the hunting scope of a niet# able brush'setfin search OanidlelifneeX- tending toa particularjoifice. While the4 1nvention 'discloses ineansfor controlling-"the extent of .trunkl hunting and thus thesize ottrunlg groupes' through thetleitfhlelocation of overflow terminals at various points in the banks of selective switch mechanism, it is not intended that the invention shall be limited to the control of oliice grouping since it has a wider utility and may be used for any form of control individual to each of a plurality of bank selecting means.

i Y That is claimed: is:

dered ooerative for Governing the extent ot said hunting movement.

211i a selector switch, a plurality of brush sets, banks of terminals associated with said brush sets respectively, the ter-A minals of each ot said banks being divided into groups, and said brush sets being normally out o'tl engagement with their asso ciated bank terminals, means for bringing any one of said brush sets into engageable relationship with its bank oit' terminals, means for advancing` the selected brush setin group and terminal hunting movements Y over the terminals of its bank, and means rendered variably effective in accordance with which one of said brush sets was rendered operative for governing the extent ot said limiting movement.

3. ln a selector-switch, a plurality ot brush sets, banks of terminals associated with said brush sets respectively, the terminals ot' each ot said banks being divided into groups and said brush sets being normally out ot engagement with their asso-v ciated bank terminals, means lor bringing any one of said brush sets into engageable relationship with its bank ot terminals, means for advancing the selected brush set in group and terminal hunting movements over the terminals ot its associated bank, anv

iiiterrnpter` controlled in the movements ot said switch, and means controlled bysaid interrnpterV for governing the extent of said hunting movement in accordance with which one of said biush sets was rendered eii'ective. At. ln a selector'switch, 'a plurality ot brush sets, banks of terminals associated with saidbrush sets respectively, the terminals of each of said banks being divided intol groups and said, brush sets being normally out of engagement with' their asso-` ciatedbank terminals, means for bringing any one of saidV brush sets'jinto engageable krelationship with its bank of terminals,

means for advancing the sk'ale'ctedr brush set in group and terminal limiting movements over the terminals oi" its bank, an interrupter controlled' in the movements of said switch, an auxiliary switch controlled by saidinterrupter, and means controlled by said anxiliary switch invaccordance with which one ot'said brush sets was rendered effective for governing the extent of said hunting -movement.

5. ln a selector switch, a. plurality of biusli sets, banks ot terminals associated with said brush sets respectively, the terminals of each oit said banks being divided into groups and said brush sets being normally out of engagement with their asso'- ciated bank terminals, means for bringing any one ot' said brushsets into engageable relationship with its bank orp terminals, means for advancing the selected brush set in group selection and terminal hunting movements over the terminals of its assolelated bank, an interrupter for said switch having overflow terminals for iioriii-ally dividing said banks into similar groups, and means rendered variably effective in accordance with which one ot said brush sets was rendered operative for rendering at will said overi'iow terminals e'ttective to change `the grouping of the terminals in said banks.

6. in a selector switch, a plurality Vot brush sets, banks of terminals associated with said brush 'setsl respectively, the terminalsl of each of said banks being' divided into gronps and said brush sets being` normally out of engagement with their associated bank terniiV nalsmeans for bringing any one of said brush sets into engageable relationship with its bank of terminals, means for advancing the selected brush set in group selection andterminal hunting movementsV over the terminals of its associated bank, an interrupter ilor said switch having overflow terminals for normally dividing said banks into similar groups, and means rendered variably etective in accordance with Awhich one of said brush sets was rendered' operative tor rendering at will said overiiow terminals ei-A `fective to, change the grouping of the terminals in any of said banks. Y

7. In a selector switch, a plugrality' of brush sets, banks of terminals associated with said brush'sets respectively, the terminals ot each of said banks being divided into groups and said brush sets being normally out of engagei'iient with their associated bank terminals, means Vfor bringingany one ofsaid brush sets into engageable relationship with its bank of terminals, means for advancing the selected'brush set in group selection and terminal hunting movements over the terminals' of its associated bank, an interrupter for said switch having overflow terminals for normally dividing said banks into similar groups, and means rendered variably effective in accordance with which bank of terminals associated withk each brush set, 'means to selectively render operative aA desired yone of said brush sets and to operate the associated oi-normal contact and .means controlled over said contact to determine the grouping of terminals in the bank associated therewith.

9. In a telephone exchange system, main groups of trunks divided into sub-groups, the sub-groups of the various main groups being non-symmetrical in capacity, means to select a desired main group and'to select a desired sub-group, an auxiliary device, and means to provide for a trunk hunting movekment of suitable extent vfor a selected subgroup, said means being` controlled by said auxiliary device in accordance vviththe main group selected.

10. In a telephone exchange system, main ygroups of trunks divided into sub-groups,

the sub-groups of the various main groups being iionsyminetrical in capacity, means to select a desired inain group and to select a desired sub-group, an auxiliaryv device provided with sections correspondingv to". each main group, means to render'elifective a corresponding section of said auxiliary device when a group of trunks is selected, and means to provide a trunkhunting movement of suitable extent for a. selected sub-group,

said means being controlled at the eiectivev Section of said auxiliary device.

11. In a telephone exchange system, a selector svvitch comprising a contact bank and a. plurality of normally inoperative multiple', brush sets-having access to said contact'bank,v

trunk lines terminating in said contactbanks in main groups, there being a main group served by each of said brush sets, sub-groups in each main group, an auxiliary device,`

means to render operative a desired one of Vsaid brush sets vto select a main group of trunks, a contact associated With each of said brush sets and operated When a brush set-y is rendered eective, sections in said auxiliary device corresponding to each main Y group, means to render eective a 'desired vsection when a brush set is rendered operative, and means to determine the maximum extent of the trunk hunting movement ofthe selector in a selected sub-group under the control of theauxiliary device f In Witness whereof, I hereuntok subscribe my name this `18th day of yJ une A. D., 1924, Y FRANK NrREEVES. 

